1. Field of the Invention
The present invention relates to a method and apparatus for applying to the skin, in a controlled manner, light to the skin in order to heat and selectively damage thin superficial layers of the skin, thereby inducing a renewal process of the epidermis.
2. Description of the Related Art
It is well known in the skin treatment art that in order to renew the epidermis layer, induced damage of the skin is required. One such method uses laser radiation that is incident on the skin and that generates several effects on the skin, depending on the wavelength of the laser radiation, the pulse duration of the laser energy applied to the skin, and the radiation energy provided to the skin.
The most commonly used method is CO2 laser radiation for generating a superficial heating of the skin. When laser light reaches the skin, its intensity decreases exponentially as it progresses down into lower layers of the skin. This means that the thermal energy that is delivered is higher in the first layer and decreases exponentially as its progresses down to lower layers of the skin. Moreover, the first corneum stratus of the skin has a higher absorption than other layers. Such an energy profile is not suitable for a uniform heating of a volume of skin due to the fact that in the superficial (upper) layers, the reached temperature is too high and in the lower layers the reached temperature is not high enough to trigger the desired skin treatment process.
Another method is to increase the temperature of the skin by heating through radiofrequency. In U.S. Pat. No. 6,269,271, which is incorporated in its entirety herein by reference, radio frequency current pulses are applied to the skin in a controlled manner in order to heat selected volumes of skin, thereby inducing the removal of unwanted pigments from the skin. A probe provides the radio frequency current pulses to the skin, where the probe includes first and second metallic stripes, and where the probe is connected to two coaxial cables that are respectively connected to the first and second metallic stripes. The two coaxial cables are connected to a balanced/unbalanced transformer, which in turn is connected to a radio frequency generator that provides radio frequency pulses.
Two principles are used in U.S. Pat. No. 6,518,538, which is incorporated in its entirety herein by reference. First, radio frequency currents are localized in the external layer of the skin due to the skin effect, and thus the heating is localized in a thin (upper) layer of skin.
It is well known that an alternating voltage applied to a conductor generates a current on the external layer of the conductor and the depth depends on the frequency and the resistance of the conductor (so-called skin effect).
Second, the plasma generated at the contact of the skin, due to the radio frequency and a high vacuum generated by a suitable pump, is composed of high energy gas ions that strike the surface of the skin, thereby generating heat in the superficial layer of the skin.
The interaction with the skin has some similarities to the interaction described in U.S. Pat. No. 6,269,271, which is incorporated in its entirety herein by reference.
One advantage of such an approach is by not having electrodes in contact with the skin, a more even distribution of the radio frequency current in the skin is achieved. Also, there is achieved a combined action from the striking gas ions and a more accurate control of the power applied to the skin surface, due to the higher impedance of the plasma that controls the current independently from the electrical conductivity value of the skin.
U.S. Pat. No. 6,518,538 describes an apparatus and a method for skin resurfacing treatment, which provides induced thermal damage of the skin by radio frequency heating and by ion bombardment of the skin.
In U.S. Pat. No. 6,518,538, this dual effect may be achieved by using a pulsed radio frequency generator connected to a probe for coupling to the skin. The probe is preferably made of a non-conductive material (such as glass or plastic), and enables the application of a high vacuum to the skin surface (e.g., 5-10 millibars) over a predetermined (e.g., round) portion of the skin, by using a non-conductive pipe connected to a vacuum pump. At a suitable distance (around 10 millimeters) from the surface of the skin, an electrode (that is housed within the probe) is used to generate a radio frequency field between the electrode itself and the surface of the skin. After reaching a sufficient vacuum (e.g., 5-10 millibars of atmospheric pressure), a high voltage radio frequency electric field is applied between the electrode and the surface of the skin, due to a radio frequency pulse applied to the electrode. Such a radio frequency field triggers a glow discharge inside the probe between the electrode and the skin. A radio frequency current, due to the low impedance of the glow discharge, flows evenly on the surface of the skin, and, due to the skin effect, is limited to the glow discharge area in a depth of about 300 microns. In the surrounding tissues, the current density decreases by the square of the distance from the area covered by the glow discharge within a depth of 300 microns. Moreover, the high energy ions of the glow discharge strike the surface of the skin, thereby providing a plasma skin resurfacing that can be used to remove spider veins, skin brown spots, or port wine stains, for example.
U.S. Pat. No. 6,518,538 describes the providing of a controlled heating of a selected portion of the skin to a depth of about 300 microns. As a result, it is possible to reach a desired temperature of 70 degrees C. or more, which triggers controlled damage to the skin cells to achieve a desired effect. The temperature reached in the described volume of the skin depends primarily on the selected pulse length and the power of the radio frequency generator. Preferably, a temperature reached in the described volume of the skin is a temperature in the range of from 75 degrees C. to 95 degrees C.
U.S. Patent Publication No. 20080021442, which is incorporated in its entirety herein by reference, describes a method and apparatus that use optical radiation to ablate or damage a target area of skin surface for dermatological treatment, which skin surface includes the epidermis and parts of the dermis as the objective or side effect of the desired treatment. In U.S. Patent Publication No. 20080021442, delivery of the electromagnetic radiation to the skin in a predetermined pattern is achieved by either masking parts of the target area of the skin surface in order to protect the masked parts of the skin surface from the electromagnetic radiation, or by utilizing a light beam of relatively small diameter which is scanned across the skin surface by various means in order to generate a specific pattern for affecting superficial thermal skin injury.
The parts of the target area of the skin surface are masked by providing a mask between a light source and the patient's skin, whereby the mask includes many small holes for allowing light to pass from the light source to the patient's skin, and whereby all other portions of the mask that do not have holes entirely block the light from passing through the mask to the patient's skin.